1. Field of the Invention
The present invention relates to an electrodeposition method light modulating device, an electrodeposition method reflective display device, and a method of manufacturing a transparent electrode for an electrodeposition method.
2. Description of the Related Art
An electrodeposition system, which is a kind of electrochromic system, is a system, in which metal is deposited on a transparent electrode, or metal on a transparent electrode is dissolved, by applying current to an electrolytic solution containing metal ions. In a state in which metal is deposited on the transparent electrode, a high light-shielding performance attributable to reflection from a mirror surface of the metal or absorption by fine particles of the metal is achieved. In contrast, in the metal ion state, a high transparency attributable to a clear and colorless electrolytic solution containing metal ions is exhibited (see U.S. Pat. Nos. 4,240,716 and 4,240,717).
In the electrodeposition method, silver, lead, bismuth, copper or the like as the metal is reversibly electroplated. In particular, when silver is used, the silver can be stably electrodeposited repeatedly, and a high light-shielding performance can be attained.
In the electrodeposition method using silver, an electrolytic solution, in which a supporting electrolyte containing a halogen and a silver halide are dissolved in an aprotic polar solvent such as N,N-dimethyl formamide (DMF) or N,N-dimethyl acetamide (DMAc), is introduced between opposing transparent electrodes. Alternatively, a polymer solid electrolyte formed by mixing the electrolytic solution with a polymer is introduced between opposing transparent electrodes.
When current is applied to the transparent electrodes, and the potential exceeds a certain potential (deposition overpotential), silver is deposited on the transparent electrode to develop color. Further, the current application is interrupted or a reverse potential is applied to the electrode, so that the silver on the transparent electrode is re-dissolved and the electrolytic solution can become transparent again.
However, in an electrochromic type light modulation system, there is a problem such that a voltage drop attributable to a high surface resistance (10Ω/□ or more) of the transparent electrode (ITO, IZO, ZnO or the like) is caused. In particular, an effective voltage is reduced in a central portion of a large-sized substrate so that metal is not deposited and an unevenness in density may arise at the time of light-shielding.
In order to cope with the problem, it has been proposed that a material for promoting a reduction reaction of metal ions is added to an electrolytic solution. For example, in Japanese Patent Application Laid-Open (JP-A) No. 2006-235484, as reduction promoting materials, hydroquinone, catechol, or the derivatives thereof, 1,4-naththalene diol, 1,5-naphthalene diol or the derivatives thereof, ferrocene, potassium ferrocyanide, or the like is proposed.
In particular, a ferrocene is stable in an electrochemical reaction, and promotes stably a reduction reaction, so that silver can be deposited even in a central portion of a large-sized substrate.
As a technique in which a ferrocene is used, for example, in JP-A No. 63-24225, a method, in which a ferrocene polymer and electroconductive fine particles are mixed with a binder, and the mixture is coated on a electrode, is proposed. In JP-A No. 10-206907, a method, in which a ferrocene carboxylic acid is amide-bonded to electroconductive particles modified with a silane having an amino group at the terminal end thereof, and the thus obtained electroconductive particles are coated on an electrode and burned, is proposed. In JP-A No. 2000-235198, a method for copolymerizing a ferrocene polymer with a polymer solid electrolyte is proposed.